( xliii ) 



form may be also a reversion, or it may be, as suggested 

 by Professor Poulton, an effort towards more conspicuous 

 coloration. If such be the case, we have here an instance of 

 accidental resemblance, a phenomenon which I cannot but 

 believe does occasionally occur. Such a suggestion will 

 probably be looked upon with disfavour by keen supporters 

 of Bates's hypothesis, but I do not see that that hypothesis 

 loses anything by the admission that every case of resemblance 

 is not necessarily true mimicry. Many other cases of im- 

 perfect resemblance might be cited which can just as easily 

 be regarded as instances of partial reversion as of incomplete 

 development. I do not necessarily insist on the theory that 

 birds have partially ceased to be a selective force acting on 

 butterflies, but I do suggest that even if it be proved that 

 they are not so now, it by no means follows that they never 

 were. 



It may be further objected that if the selective force of 

 birds is no longer as strong as it was, what influence main- 

 tains those accurate cases of mimicry with which we are all 

 familiar 1 To this one may reply that we are ignorant of the 

 7'elative power of the forces which guide development. So 

 long as existence depended upon favourable variation, sexual 

 selection may have been too weak to prevent such variation. 

 Sexual selection may, however, be suflicient in some species 

 to maintain facies which have been perfected through long 

 periods of evolution. Such suggestions are merely specu- 

 lative, but they may serve to remind those who would lay 

 down laws for mimetic development, how complicated both in 

 their nature and in their efli'ect, are the influences which guide 

 the course of evolution. 



In discussing the Batesian and Mlillerian theories. Prof. 

 Packard's paper lays much stress on the explanation that 

 resemblance between butterflies is due to convergence brought 

 about by similarity in their surroundings. Thus we read — 

 " From the facts regarding these local varieties thus stated 

 by Bates, we seem warranted in ascribing the mimetic re- 

 semblance to convergence, or exposure to the same conditions 

 of light, heat, moistvire, etc., affecting all the individuals of a 

 variety simultaneously rather than to what is vaguely called 



